Method and apparatus for controlling hydraulic systems

A control system for hydraulic actuating systems having hydraulic pressure supply and pressure return, at least one control line for applying actuating hydraulic pressure to at least one movable element, and valve means connected between said pressure supply and said control line, for controlling pressure flow therebetween, comprising:

• means for precisely actuating said valve means including stepping motor means, actuating linkage means connected between said valve means and said stepping motor means, and driver means for controlling the operation of said stepping motor means by supplying DC current through each of the windings of said stepping motor means and controlling said DC current in each of said windings;
• wherein a fluid motor and variable displacement pump whose fluid output drives said fluid motor are provided, said movable element forming the swash plate of said variable displacement pump;
• and
• wherein said fluid motor includes a rotatable output shaft, means are provided to monitor the rotational speed of said output shaft and provide feedback signals representative thereof, digital computer means are provided to receive said feedback signals and provide control signals to said driver means for adjustment of the displacement of said swash plate according to a two part computer program algorithm which initially drives said stepping motor means, through said driver means, to quickly achieve a rough approximation of the desired swash plate position and then provides revised control signals, representative of at least one of a plurality of said feedback signals and representative of at least one of a plurality of known characteristics of the control system and the hydraulic actuating system, which cause said swash plate to precisely achieve said desired swash plate position by limited modulation about said position.

A method of controlling a hydraulic system for providing motive force, including a hydraulic fluid supply, at least one control line for applying hydraulic pressure to move at least one movable element, and valve means for controlling the flow of hydraulic fluid connected between said fluid supply and said control actuating means for said valve means line, comprising:

• applying an initial control signal representative of a desired position of said movable element to said actuating means;
• calculating the difference between said desired position and the actual position of said movable element to obtain an error signal;
• continuing to apply said initial control signal to said actuating means until said error signal reaches a predetermined level;
• calculating a revised control signal necessary to produce zero error signal as a function of at least one of a plurality of known hydraulic system characteristics, when said error signal reaches said predetermined level;
• and
• applying said revised control signal to said actuating means.

A method for controlling a hydraulic system, which includes means for adjusting a condition of the system, comprising:

• applying an initial control signal, representative of a desired system condition, to said means for adjusting the condition of the system;
• generating a control signal representative of an actual system condition;
• calculating an error signal from said initial control signal and said actual system condition control signal;
• continuing to apply said initial control signal to said means for adjusting the condition of the system until said error signal reaches a predetermined level;
• calculating a revised control signal as a function of at least one feedback signal and as a function of at least one known characteristic of the system after said error signal reaches said predetermined level;
• and
• applying said revised control signal to said means for adjusting the condition of the system to precisely attain said desired system condition.